1. Technical Field of the Invention
The present invention relates generally to a method of producing a coil made up of rectangular wave-shaped windings for use in an electric rotary machine such as a motor-generator for automotive vehicles.
2. Background Art
Japanese Patent First Publication Nos. 11-285216 and 2003-18778 teach an electric rotary machine which may be employed an electric motor and/or an electric generator. The rotary machine is equipped with stator windings made up of U-shaped segment conductors which are disposed in slots formed in a stator core and have ends joined to each other electrically.
Each of the segment conductors of the electric rotary machine, as taught in the former publication, is twisted at the center (i.e., a bend) thereof to insert legs or tines thereof into two of the slots arrayed in a circumferential direction of the stator core, thus resulting in an increased height of portions (usually called coil ends) of the stator windings which protrude from the ends of the stator core. In other words, the coil ends protrude from the stator core undesirably.
In the electric rotary machine, as taught in the latter publication, the bend of each of the segment conductors is shaped in the form of a crank without being twisted in order to minimize the height of the coil ends.
In the case where the rotary machine of the former publication is designed to have the slots arrayed at a constant interval away from each other and the segment conductors of the same thickness, triangles each defined by the coil end of the segment conductor and the end of the stator will be identical in length of the base and base angle with each other. The rotary machine of such a type has, therefore, a limitation to decreasing the height of the coil ends.
The height of the coil ends may be decreased by making the coil with a single flat wire to eliminates joints of the segment conductors on the end of the stator core and shaping the coil ends to be stepwise in an axial direction of the stator core to have the height thereof which is a multiple of width of the flat wire.
If the coil is made of a single wire, as described above, the wire needs to be folded to mount the coil in the stator core, which may cause undesirable deformation of the coil. The folding of the wire also results in a difficulty in shaping the coil ends to be stepwise due to physical interference between adjacent segments of the folded wire.